/* SPDX-License-Identifier: LGPL-2.1-or-later */

#include <errno.h>
#include <signal.h>
#include <stddef.h>
#include <sys/mman.h>

#include "macro.h"
#include "memory-util.h"
#include "sigbus.h"

#define SIGBUS_QUEUE_MAX 64

static struct sigaction old_sigaction;
static unsigned n_installed = 0;

/* We maintain a fixed size list of page addresses that triggered a
   SIGBUS. We access with list with atomic operations, so that we
   don't have to deal with locks between signal handler and main
   programs in possibly multiple threads. */

static void* volatile sigbus_queue[SIGBUS_QUEUE_MAX];
static volatile sig_atomic_t n_sigbus_queue = 0;

// static void sigbus_push(void *addr) {
//         assert(addr);
// 
//         /* Find a free place, increase the number of entries and leave, if we can */
//         for (size_t u = 0; u < SIGBUS_QUEUE_MAX; u++)
//                 if (__sync_bool_compare_and_swap(&sigbus_queue[u], NULL, addr)) {
//                         __sync_fetch_and_add(&n_sigbus_queue, 1);
//                         return;
//                 }
// 
//         /* If we can't, make sure the queue size is out of bounds, to
//          * mark it as overflow */
//         for (;;) {
//                 unsigned c;
// 
//                 __sync_synchronize();
//                 c = n_sigbus_queue;
// 
//                 if (c > SIGBUS_QUEUE_MAX) /* already overflow */
//                         return;
// 
//                 if (__sync_bool_compare_and_swap(&n_sigbus_queue, c, c + SIGBUS_QUEUE_MAX))
//                         return;
//         }
// }

int sigbus_pop(void **ret) {
        assert(ret);

        for (;;) {
                unsigned u, c;

                __sync_synchronize();
                c = n_sigbus_queue;

                if (_likely_(c == 0))
                        return 0;

                if (_unlikely_(c >= SIGBUS_QUEUE_MAX))
                        return -EOVERFLOW;

                for (u = 0; u < SIGBUS_QUEUE_MAX; u++) {
                        void *addr;

                        addr = sigbus_queue[u];
                        if (!addr)
                                continue;

                        if (__sync_bool_compare_and_swap(&sigbus_queue[u], addr, NULL)) {
                                __sync_fetch_and_sub(&n_sigbus_queue, 1);
                                *ret = addr;
                                return 1;
                        }
                }
        }
}

// static void sigbus_handler(int sn, siginfo_t *si, void *data) {
//         unsigned long ul;
//         void *aligned;
// 
//         assert(sn == SIGBUS);
//         assert(si);
// 
//         if (si->si_code != BUS_ADRERR || !si->si_addr) {
//                 assert_se(sigaction(SIGBUS, &old_sigaction, NULL) == 0);
//                 raise(SIGBUS);
//                 return;
//         }
// 
//         ul = (unsigned long) si->si_addr;
//         ul = ul / page_size();
//         ul = ul * page_size();
//         aligned = (void*) ul;
// 
//         /* Let's remember which address failed */
//         sigbus_push(aligned);
// 
//         /* Replace mapping with an anonymous page, so that the
//          * execution can continue, however with a zeroed out page */
//         assert_se(mmap(aligned, page_size(), PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS|MAP_FIXED, -1, 0) == aligned);
// }

// void sigbus_install(void) {
//         struct sigaction sa = {
//                 .sa_sigaction = sigbus_handler,
//                 .sa_flags = SA_SIGINFO,
//         };
// 
//         /* make sure that sysconf() is not called from a signal handler because
//         * it is not guaranteed to be async-signal-safe since POSIX.1-2008 */
//         (void) page_size();
// 
//         n_installed++;
// 
//         if (n_installed == 1)
//                 assert_se(sigaction(SIGBUS, &sa, &old_sigaction) == 0);
// 
//         return;
// }

void sigbus_reset(void) {

        if (n_installed <= 0)
                return;

        n_installed--;

        if (n_installed == 0)
                assert_se(sigaction(SIGBUS, &old_sigaction, NULL) == 0);

        return;
}
